1. Field of the Invention
The present invention relates to an optical disk recording and reproducing apparatus and a method which perform a brake operation by a tracking servo and also relates to a tracking servo apparatus and a method of an optical disk drive apparatus.
2. Description of the Related Art
A so-called CD (compact disk), on which an audio signal is recorded, has come into wide use, and further an optical disk which is large in data capacity and high in recording density is highly required.
In order to increase the recording density of an optical disk, the track pitch thereon is narrowed to thereby increase the recording density of the optical disk. For example, the track pitch of a CD is 1.6 .mu.m, while the track pitch of a so-called DVD (digital video disk or digital versatile disk) having a capacity about 7 times of the CD is 0.74 .mu.m. Due to the narrow track pitch and high compressing technology, the DVD has the recording desity about 7 times the recording density of the CD.
By the way, as the track pitch of the optical disk becomes narrower, there is easily caused a so-called track jump by a vibration or impact (here, vibration and impact are all together referred to as a shock) from the outside. Therefore, it is necessary that, in a disk drive apparatus which drives an optical disk with a narrow track pitch, the track jump caused by the shock applied to its optical pickup (optical head) from the outside is suppressed.
In a tracking servo apparatus of a conventional optical disk drive apparatus, after the tracking servo is effected or taken in and after the track jump, a brake is applied to a lens actuator which drives an objective lens.
Then, a tracking servo apparatus of a conventional optical disk drive apparatus, in which a brake is applied to a tracking servo, will be now described with reference to FIG. 6 which shows an arrangement of an example of the present invention described later on and FIG. 7 which shows its timing chart used for explaining its operation. In FIG. 7, the timing chart when a light beam from an objective lens moves from the inner periphery of an optical disk to its outer periphery in the radius direction is shown in the left side, and the timing chart when the light beam moves from the outer periphery to the inner periphery of the optical disk is shown in the right side.
The optical disk has grooves of concentric circles or a groove of spiral shape and information is recorded on the bottom of groove or a land to form a pit series. As shown in FIG. 6, a detecting signal (RF(radio frequency)signal) A form a photo-detector of an optical pickup (optical head) in the optical disk drive apparatus is supplied to an envelope detection and filter process circuit 31, its envelope is detected, and its detected output is filter-processed to remove noise components thereof. An envelope detected output B, from which noise components are removed, from the circuit 31 is supplied to a zero-cross comparator circuit 32 to provide a land/groove discrimination signal C. These circuits 31 and 32 form a land/groove discrimination signal generating circuit.
Meanwhile, as the land/groove discrimination signal generating circuit, in addition to the above-mentioned circuit, there may be a low pass filter which is supplied with the RF signal to generate a land/groove discrimination signal, a phase difference detecting circuit which is supplied with a light detecting signal of two reproduced light beams reflected from an optical disk to generate a land/groove discrimination signal, and so on.
The land/groove discrimination signal C obtained from the zero-cross comparator circuit (zero-cross comparator) 32 has a rectangular waveform indicated by C in FIG. 7 in which a high (H) level shows a land portion, while a low (L) level shows a groove portion, respectively. The land/groove discrimination signal C is supplied to a D flip-flop 36 at its D input terminal, and a zero-cross edge signal G of a tracking error signal D (whose waveform is not shown in FIG. 7) is supplied to the clock input terminal of the D flip-flop 36 which samples the land/groove discrimination signal C by the zero-cross edge signal G of the tracking error signal D to produce a brake operation timing signal H at its noninverting output terminal.
Next, the circuit which generates the zero-cross edge signal G of the tracking error signal D will be now described. The tracking error signal D is supplied to a filter process circuit 33 which produces a tracking error signal E from which noise components are removed. This tracking error signal E is supplied to a zero-cross comparator circuit 34. A compared output F from this zero-cross comparator circuit 34 is supplied to an edge detecting circuit 35 which then produces the zero-cross edge signal G which indicates a rising edge and a trailing edge of the tracking error signal D.
The brake operation timing signal H is a rectangular waveform signal as shown in FIG. 7. Its high level indicates a cut-off state of the tracking servo loop, while its low level indicates an operation state of the tracking servo loop.
The tracking error signal D is further supplied to a tracking servo filter process circuit 38 in which its noise components are removed and then is outputted as an actuator drive signal I through a change-over switch 39. A brake operation ON/OFF signal, which goes to a high level when the brake is in an ON-state while goes to a low level when the brake is in an OFF-state, and the brake operation timing signal H are supplied to an AND-gate 37. The changing operation of the change-over switch 39, which changes over the output from the tracking servo filter process circuit 34 and a zero level (ground level), is controlled by the output from the AND-gate 37 such that when the output of the AND-gate 37 is in high level, the tracking error signal, whose noise components are removed, from the tracking servo filter process circuit 38 passes through the change-over switch 39 to become the actuator drive signal I, while when the output of the AND-gate 37 is low in level, the passing of the tracking error signal with no noise components through the change-over switch 39 is rejected and the actuator drive signal I becomes the zero level (ground level).
With reference to the actuator drive signal I shown in FIG. 7, when the brake is applied to the actuator, the relative velocity between the optical disk and the lens actuator becomes nearly zero and the tracking servo is easily taken in. Thus, the brake to the lens actuator is operated upon the tracking servo being taken in at first and the tracking servo being taken in after the track jump. During the recording or reproducing operation on or from the optical disk which is in a state that the tracking servo is taken in, the brake operation is released.
The tracking error signal during the recording or reproducing operation on or from the optical disk is nearly zero, so that a noise is easily contained in the zero-cross signal F of the tracking error signal D. Further, since the envelope detecting signal B of the FR signal, which is a base of the land/groove discrimination signal C during the recording or reproducing operation on or from the optical disk, is less in fluctuation, noise components are easily contained in the land/groove discrimination signal C at its portion near the zero level. Under the influence of noise components of these signals, the brake is operated during the recording or reproducing operation for the optical disk to release the tracking servo, and hence the tracking error is increased thereby.
According to the tracking servo apparatus of the optical disk drive apparatus which drives an optical disk narrow in track pitch and large in recording density, as described before, the tracking servo comes off by a large vibration or a large shock applied to the optical pickup (optical head) from its outside and hence the track jump is caused easily. Once the track jump is caused, the tracking servo, which is effected in a tracking servo range of the tracking error signal, is effected in a tracking non-servo range opposite in polarity to the tracking servo range of the tracking error signal and hence the track jump occurs frequently. In order to minimize such a track jump, it is necessary that when a track jump appears, the servo applied to the lens actuator is made off to apply a brake to the lens actuator. The track jump is minimized by the brake to thereby make it possible that a return time period of the tracking servo after the vibration and shock are applied to the optical pickup from the outside is shortened, the excess drive of lens actuator is suppressed, and a trouble of the lens actuator can be avoided. It is necessary that when the vibration and shock are applied to the optical pickup from the outside, a brake is applied to the lens actuator rapidly.
However, due to the fact that the track pitch becomes narrower, when vibration and shock are applied from the outside, a so-called track jump is easily caused exceeding a track range. In the recording and reproducing of an optical disk with a large data capacity, since its track pitch is narrow, it is easily affected by the vibration and shock from the outside.
Especially, when a large shock is applied to an apparatus from its outside, a tracking servo comes off with ease and hence a track jump is generated. Once the track jump appears, an unnecessary output outside the tracking servo range is applied which increases the track jump successively.
Therefore, in the recording and reproducing of the optical disk large in data capacity, such a measure is necessary that even if a shock is applied, its influence is reduced.
In order to minimize the track jump, the tracking servo should perform a brake operation. By minimizing the track jump, the return time period after the shock being applied from the outside can be shortened and also the excess drive of the actuator can be suppressed to avoid the trouble of the apparatus. To this end, it is required such a measure to immediately initiate the brake operation upon the application of shock.